We have developed a method for measuring filtration and estimating ultrafiltration coefficient in single isolated glomeruli in vitro. We have applied this technique to the study of ultrafiltration characteristics of glomeruli of rats, rabbits, dogs and sheep. We have documented a relationship between glomerular size and ultrafiltration coefficient in growing rats, rabbits and dogs as well as when these species are compared. Further studies will be carried out to better define the relationship between ultrafiltration coefficient and capillary surface area and endothelial fenestral area in the glomeruli of several species. We have also documented that volume depletion produces a reversible decrease in ultrafiltration coefficient. We will continue to study the effect of intravascular volume depletion on glomerular function as well as studying the effects of individual humoral mediators which may play a role in the response to volume depletion. We have established conditions which permit the incubation of glomeruli with humoral agents in vitro and will study the effect of several vasoactive agents including angiotensin II on glomerular size and filtration in vitro. In addition we will study the effects of specific blockers for each mediator which effects glomerular function in vitro. The studies will enhance our understanding of normal glomerular filtration and the mechanisms which modulate glomerular function in physiologic and pathologic states.